1. Field of the Invention
The present invention relates to a liquid crystal display and a panel for a liquid crystal display, more particularly, to a vertically aligned liquid crystal display which has opening patterns and projections formed at pixel electrodes, and a thin film transistor (TFT) array panel therefor.
2. Description of the Related Art
Generally, a liquid crystal display includes an upper panel having a common electrode and color filters, a lower panel having TFTs and pixel electrodes, and a liquid crystal layer between the two panels. The pixel electrodes and the common electrode are applied with different electric potentials to form electric fields, which change the alignment of liquid crystal molecules to control the light transmittance, thereby displaying images.
However, a liquid crystal display has a serious disadvantage that its viewing angle is narrow. To overcome this disadvantage, various techniques for widening the viewing angle are suggested. Among them, there is a technique that the liquid crystal molecules are aligned vertical to the upper and the lower panels and opening patterns or projections are provided in pixel electrodes and a common electrode facing the pixel electrodes.
In a conventional technique of providing the opening patterns, the opening patterns are formed in both the pixel electrodes and the common electrode to generate fringe field. The tilt directions of liquid crystal molecules are adjusted by using the fringe field.
However, the above conventional technique requires an additional photolithography process for pattering the common electrode of indium-tin-oxide (ITO) on the color filters to form the opening patterns.
Furthermore, the adhesive strength between the color filters of resin and the common electrode of ITO deposited on the color filters by sputtering is bad and hence the etching precision of the common electrode is poor. In addition, in order to prevent the damage in the color filters exposed when etching the ITO, the color filters are generally coated with a reliable overcoat film of organic insulating material which is very expensive. When the overcoat film is adapted between the color filters and the common electrode, the common electrode cannot be in direct contact with the black matrix of chrome (Cr) which is generally disposed under the overcoat film, thereby increasing the resistance to raise flicker. Also the opening pattern of the common electrode causes the resistance of the common electrode to be increased.
On the other hand, there is a difficulty in precisely aligning the opening pattern formed in the common electrode of the upper panel with that formed in the pixel electrodes of the lower panel when assembling the upper and the lower panels.
A conventional technique of providing projections is that the tilt directions of the liquid crystal molecules are adjusted by using electric field distorted by the projection formed in both the common electrode of the upper panel and the pixel electrode of the lower panel.
However, the above method has problems that the product cost increases due to additional processes of forming the projections in the upper and the lower panels and that the projections in the respective panels have to be precisely aligned.
There is another conventional technique that opening patterns and the projections are provided in the pixel electrodes on the lower panel and the common electrode on the upper panel, respectively, to generate fringe field. The tilt directions of the liquid crystal molecules are adjusted by using the fringe field, thereby forming domains.
However, the above technique has difficulties in precisely aligning the projection and the opening pattern when assembling the upper and the lower panels as well as adding the process of forming the projections on the common electrode.
Furthermore, when the projections or the openings are adapted to control the tilt directions of the liquid crystal molecules, texture is created due to the disordered alignment of the liquid crystal molecules around the projections or the openings. This texture brings about light leakage and produces a bad effect on picture quality.